Concrete ties have been in use in some parts of the world for a long time but it is only since 1985 that they have been able to provide cost benefits for use in North America relative to wooden ties.
One advantage of concrete ties is that the rail seats can be pre assembled with only a few components to be added on site when the rail is placed in position. The difficulty with this is that the pre assembled components can become dislodged during transport and some components still have to be positioned on the rail. The rail seats usually comprises a rail pad that is positioned below the rail, an abrasion resistant plate below the pad, rail clip support shoulders on the field and gauge sides of the rail, an elastic rail clip that seats in the support shoulder and bears down on the rail base and an insulator that lies between the rail and the rail clip and the support shoulder. The support shoulders are precast in the rail tie and the rail pad is fitted between each pair. Because the rail clips and insulators contact the rail when fastened they cannot be placed in position until the rail has been placed in position on the rail seat. Rail seat assemblies of this type have been generally described in U.S. Pat. Nos. 5,110,046, 5,551,633 and 6,604,690. The rail clips in these assemblies are either installed or loose and therefore had to be assembled on site. U.S. Pat. No. 6,367,704 proposed using a modified support shoulder so that the clip could be partially installed for transport purposes where it was retained on the shoulder and then able to be fully installed when the rail was placed in position. In this arrangement the insulators still needed to be placed in position manually before the clip could be fully installed. U.S. Pat. No. 5,520,330 discloses a bent rod rail clip with a two part insulator that enables the rail seat to be pre-assembled at the tie plant.
WO02/31264 discloses a rail clip that has an insulator encapsulating the toe of the rail clip that lies on the rail flange to avoid the need to insert the insulator separately.
One concern with concrete rail ties is the cost and it is desirable to reduce the cost of the assembled rail tie. One significant component in the cost of the rail tie is the clip support shoulder embedded in the concrete rail tie. This support shoulder needs to be durable and capable of withstanding the forces applied by the rail clip. The rail clip applies a high clamping force of 8 to 13 kilonewtons and this force is achieved by gradually displacing the toe of the clip from the base by driving the clip horizontally along a loading surface in the support shoulder. The clip reaction against the base of the support shoulder is very high and approaches pressures where metal pickup occurs. The force required to fit the clip is usually inversely linked to the length the clip travels within the shoulder. Thus the support shoulders are usually large to reduce the force needed to apply the clips and the size of the shoulders is proportional to their cost. When the support shoulders are designed to accept preloaded clips, as part of a partly assembled rail seat prior to the rail being fitted, extra travel distance is required because in the preloaded position the toe of the clip must be clear of the rail. This additional length increases the size and cost of the support shoulders.
It is an object of this invention to provide a rail clip shoulder that is less expensive and enables easier assembly of a rail seat with high clamping forces without compromising rail fastening performance.